2004 Engine computer problem?

[svtslowcar]

here is my situation. I have a 2004 cobra using a diablo predator tuner. i have no cats on my car , b/c i went with a Dr. Gas o/r pipe, so now my service engine light is on, so i use my tuner to elimnate that. it works right after the intial install of the tune to eliminate the 02' sensors. but when i park my car and get back in it 15 minutes later, the service engine light is back on. is my engine compuer resetting itself & not taking the tune?

im just wondering this b/c i had a 2.75 upper pulley on this car & it ran perfectly fine the 1st time we installed the 91 octane pulley tune with the diablo tuner, then the next day after i started my car up & got on the gas, i had bad detonation, & couldnt make boost over 12 lbs or my engine would detonate, and im wondering if this is b/c my engine computer keeps resettig itself or just rejects the diblo predator tune? so i just put on a 2.93 pulley to be safe now. i follow all the instructions that the tuner says and ive never had an error message when its finished with installing its tune? please help me, any advice is very appreciated, as i want to get a ported eaton soon, but if my computer is messed up theres no point b/c it wont run right. thanks for the help

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[Juggernaut]

sounds like you have a previous tune installed

 

[Oncebitten03]

If you bought it used check to see if there's a chip in the computer already

 

[svtslowcar]

If you bought it used check to see if there's a chip in the computer already

i dont think ther was a chip installed, but i willinspect it again, i bought it with 5800 miles on it, complete stock. and if it did have a chip or aprevious tune in it, shouldnt the new tune have overwritten the old 1?. i bought the tuner brand new from RPM outlet. would you suggest me putting th stock tuen back in, then putting the 91 pulley octane back in again & then try to modify the parameters again, to shutoff the 02' sensor. thanks, i was also planning on callin ford & diablo abou this as sooon as the holiday is over with. thanks agin & any further suggestions/advice/help is much apreciated.